Why Do Planes Fly So High?

Why Do Planes Fly So High?


[SciShow Intro] You frequent flyer types are probably used to it, but the fact is, when we travel by air, we are way up there. The average cruising altitude of a commercial jet is 7 1/2 to 11 kilometers. In horizontal terms, that is at least as far as the average distance between you and the nearest Starbucks at any given moment. In vertical terms, well, that’s a long way down. The good news is that the place starts to fall and has a long time to figure out how to stop falling. But we’ve been flying that high ever since the development of the jet engine in the mid-1950s. And jets were designed to fly at these high altitudes because there’s less air up there. And that’s what engineers,
passengers, and airlines all prefer. Basically, there are far fewer air molecules at say 30,000 feet or 9 kilometers than at sea level, so the plane is literally running into fewer molecules. This means it doesn’t have to produce as much thrust in order to maintain the speed necessary to fly. So it can travel more efficiently, which is what the airlines want. What the passengers want is to not feel
like they’re flying in the air at all, and flying at higher altitudes means being able to fly over at least some
of the weather patterns and air currents that older, less powerful propeller planes
often had to fly through. So flying higher usually means a more comfortable flight. But there are some trade-offs
for this efficiency and comfort. In order to stay in the air, an airplane needs to maintain lift, the force that counteracts its weight. At lower altitudes, having lots of air around
helps a plane get lift, but the higher it goes, the harder it is to maintain. So engineers have to find ways to generate more lift in other ways, like making planes with larger wings. Jets can’t fly too high, though. In order to like continue working, jet engines need to burn fuel. That is an important part of the process, and to burn stuff, you need oxygen. So planes have to stay at altitudes where there’s still enough oxygen to mix with the jet fuel, and allow combustion to happen. To get any higher, your aircraft would have to pack canisters of air to mix with the fuel, and once you do that, you’re not an airplane anymore; you’re basically a rocket. So engineers have done the math and found the optimal height for efficient travel, and designed planes to operate best at that height. Yay engineers! Thanks to our friends on tumblr who asked this question. Thank you to our Patreon patrons who keep these answers coming. If you’d like to submit questions to be answered, or get these quick questions a few days before everyone else, you can go to patreon.com/scishow [SciShow Outro]

Danny Hutson

100 thoughts on “Why Do Planes Fly So High?

  1. Why people use gasoline instead of hydrogen? Gasoline exhaust fuel are poisonous and bad for nature and when hydrogen burn the only exhaust is water?

  2. I hate planes they scare me, even though I've travelled from Spain to New Zealand which is basically a 180 degree movement around the world.

  3. Also taking advantage of air currents. If you travel with the current, your true speed is higher than your air speed. If you are traveling 50mph in the same direction as a 50mph wind, you have 0mph airspeed, 50mph true speed. No lift, you fall down. Lets say a certain aircraft has a cruise speed of 500mph. If you have no wind, 0mph wind speed, your air and true speed will be "the same". If you have a 100mph air current traveling the same direction as you, you can either throttle back to maintain a 500mph true speed while having a 400mph air speed, saving fuel, OR you can maintain roughly the same throttle and have your 500mph air speed while attaining a 600mph true speed. In actuality there is more involved in the calculation, but it gives a rough idea. Albeit, conversely, traveling against your 100mph air current you will either have to throttle up to 600mph air speed (if it doesn't exceed your "Do-Not-Exceed Speed") burning more fuel to maintain 500mph true speed, or compromise to achieve 500mph air speed and 400mph true speed.

  4. HEY!! I work on a propellor plane and its just turned 1. Propellor planes are not 'older, less efficient' for traveling smaller distances they are way more efficient so airlines keep buying new propellor planes for flight times between 40 minutes and 3 hours

  5. There's no generic optimal altitude for cruise. With every new generation of airliners, they tend to fly higher and higher.
    That's a result of each new generation of airliners coming with more powerful engines vs the max takeoff weight of the aircraft.
    Newer engines also use less fuel, which allows wings to become thinner.
    That allied with wings tuned for lower high subsonic drag allows planes to go a little faster, that extra speed also generates more lift.
    Consider the old 737 cruised in the Mach 0.70-0.74 range and in the 30-35 thousand ft altitude. The new ones cruise at Mach 0.78-0.81 and 35-42 thousand ft altitude.
    The first generation 767 cruised at Mach 0.80. The latest successor, the B787 cruises at Mach 0.85. And average cruising altitudes also increased by about 4000 ft.
    But there is a limit. In practice, airlines flying above 43000ft is problematic, the air is so thin that if there's a decompression there's too little time for the pilots to put an oxygen mask safely, and the pressurization differential gets a bit too high, increasing wear on the aircraft long term. But biz jets are capable to fly as high as 51000ft, where those turbo fans literally sip fuel like half the fuel consumption at 38000ft. But one pilot is required to use an oxygen mask continuously at such high altitudes.

  6. I love how you guys just jump into the answer right away instead of giving bs and rhetorical questions for the first two minutes like most science channels!

  7. THIS is why high-speed trains aren't all that. You can't travel as fast, as efficiently, because you're pushing ground-level air aside. The best you can do is travel at 1/3 the speed (170 MPH or so), and hope the lessened need for security (quicker boarding) makes up for the longer transit times. This means you really don't want to travel more than about 800 miles or so by train.

  8. I was expecting more of a scientific analysis. Like why airplanes go up quickly then kind of coast/drift towards landing due to engine efficiency and such. Also, something to do with engine by-pass ratios and engine sizing per mass.

  9. i accidentally timed the outro music with the last episode i was watching with the intro music in this one.

  10. Jesus this a video about why planes fly so high not was 9/11 an inside job or can jet fuel weaken steal beams just quit arguing about conspiracies on an educational video on why planes fly at the altitude they do

  11. but in his video about why it can be too hot to fly planes, he said more molecules helps, but now he's saying less molecules helps. WHY HANK???? WHY????

  12. I wonder, as these planes get more fuel efficient couldn't they fly higher (at the expense of the efficiency) in order to bypass even more of the weather/turbulence?

  13. Simple, thinner air up there, less air resistance, more speed without as much lift. If u went that speed at lower height the lift would bring it up a lot.

  14. 😐 please a bit slower speak. i could undrestand what did you said. just think people from the world want know this information , not just that people from your country …
    thanks

  15. At high altitude i.e from 7000to 12000m the plane comes under turbulence effect.
    But at low heights it doesn't.
    So how does flying high is comfortable?
    You can watch videos of airlines where passengers feel great discomfort due to turbulence.
    This would have been avoided if the plane would have travelled close to ground.

  16. There is a comment here about jet fuel melting steel, and a horrible answers was given. I was just wondering if anyone seen the footage of 9/11 what was that gigantic orange ball outside the tower. Heat always rises and what would any of this have to do with beams,oh, say,100 feet below impact. Hey YT scientists just sayin.

  17. So if the earth has an energy shift as expected soon, wont the planes just start falling from the sky??? 🤷🏿‍♂️

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